(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method for providing a protective layer over the surface of a created copper interconnect.
(2) Description of the Prior Art
An important aspect in the creation of semiconductor devices is the interconnect metal that is provided between elements of semiconductor devices or between semiconductor devices. Interconnect metal typically comprises metal conductive lines and vias that provide the interconnection of integrated circuits in semiconductor devices and/or the interconnections in a multilayer substrate over the surface of which semiconductor devices are mounted. Frequently used processes for the creation of conductive interconnects are the single damascene and the dual damascene processes. In fabricating Very and Ultra Large Scale Integration (VLSI and ULSI) circuits with the dual damascene process, a layer of insulating or dielectric material, comprising for instance silicon oxide, is patterned with several thousand openings. These openings form the pattern for the conductive lines and vias, which are filled at the same time with metal, such as typically aluminum but more recently copper. The pattern of conductive lines and vias serves to interconnect active and passive elements of an integrated circuit. The dual damascene process also is used to form multilevel conductive lines of metal, such as copper, in layers of insulating material, such as polyimide, using therewith multi-layer substrates over the surface of which semiconductor devices are mounted.
Single damascene is an interconnection fabrication process in which grooves are formed in an insulating layer and filled with metal to form the conductive lines. Dual damascene is a multi-level interconnection process in which, in addition to forming the grooves of the single damascene process, conductive via openings also are formed. In the standard dual damascene process, the insulating layer is coated with a layer of photoresist. The coated layer of photoresist is first exposed through a first mask with an image pattern of the via openings, the via pattern is anisotropically etched in the upper half of the insulating layer. The photoresist now is second exposed through a second mask with an image pattern of conductive lines after the second exposure has been aligned with the first exposure pattern in order to encompass the via openings. In anisotropically etching the openings for the conductive lines in the upper half of the insulating material, the via openings that have previously been created in the upper half of the insulating layer are simultaneously etched and replicated in the lower half of the insulating material. After the etching of the conductive lines and the vias is complete, both the vias and line openings are filled with metal.
The dual damascene process is an improvement over the single damascene process because the dual damascene process permits the filling of both the conductive grooves and vias with metal at the same time, thereby eliminating processing steps. Although the standard damascene process offers a number of advantages over other processes for forming interconnections, it has a number of disadvantages. For instance, the dual damascene process requires two masking steps to form the pattern, a first mask for the vias and a second mask for the conductive lines. Further, the edges of the via openings in the lower half of the insulating layer, after the second etching, tend to be poorly defined because of the two etchings. In addition, since alignment of the two masks is critical in order for the pattern of the conductive lines to be aligned with the pattern of the vias, a relatively large tolerance is provided resulting in via openings that do not extend over the full width of the conductive line.
Copper is gaining increased use as an interconnect metal due to its low cost and low resistivity. Copper however has a relatively large diffusion coefficient into a surrounding dielectric material such as silicon dioxide and silicon. Copper, which is used as an interconnect medium, therefore readily diffuses into the silicon dioxide layer causing the dielectric to become conductive and decreasing the dielectric strength of the silicon dioxide layer. Copper interconnects are therefore typically encapsulated by at least one diffusion barrier to prevent diffusion into the surrounding silicon dioxide layer. Copper is also well known to be very sensitive to surface exposure, typically resulting in oxidation of the exposed copper surface.
The invention addresses concerns of creating copper interconnects and, more specifically, the negative impact that is experienced by an exposed surface of created copper interconnects.
U.S. Pat. No. 6,180,516 B1 (Hsu) shows a lift off process for a barrier layer in a dual damascene process.
U.S. Pat. No. 5,689,140 (Shoda) shows a lift off process for a barrier layer in a dual damascene process.
U.S. Pat. No. 6,202,191 (Filippi et al.) shows a lift off process for an inductor.
U.S. Pat. No. 6,281,127 B1 (Shue) shows a self passivation process for a dual damascene interconnect.
U.S. Pat. No. 6,274,499 (Gupta et al.) shows a cap over an interconnect.
U.S. Pat. No. 6,258,713 B1 (Yu et al.) discloses a dual damascene with a cap.